i40e/i40evf: Update code to better handle incrementing page count

Update the driver code so that we do bulk updates of the page reference
count instead of just incrementing it by one reference at a time.  The
advantage to doing this is that we cut down on atomic operations and
this in turn should give us a slight improvement in cycles per packet.
In addition if we eventually move this over to using build_skb the gains
will be more noticeable.

I also found and fixed a store forwarding stall from where we were
assigning "*new_buff = *old_buff".  By breaking it up into individual
copies we can avoid this and as a result the performance is slightly
improved.

Change-ID: I1d3880dece4133eca3c32423b04a5467321ccc52
Signed-off-by: Alexander Duyck <[email protected]>
Tested-by: Andrew Bowers <[email protected]>
Signed-off-by: Jeff Kirsher <[email protected]>

Author: Alexander Duyck

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -1154,7 +1154,7 @@ void i40e_clean_rx_ring(struct i40e_ring *rx_ring)
 				     PAGE_SIZE,
 				     DMA_FROM_DEVICE,
 				     I40E_RX_DMA_ATTR);
-		__free_pages(rx_bi->page, 0);
+		__page_frag_cache_drain(rx_bi->page, rx_bi->pagecnt_bias);
 
 		rx_bi->page = NULL;
 		rx_bi->page_offset = 0;
@@ -1299,6 +1299,7 @@ static bool i40e_alloc_mapped_page(struct i40e_ring *rx_ring,
 	bi->dma = dma;
 	bi->page = page;
 	bi->page_offset = 0;
+	bi->pagecnt_bias = 1;
 
 	return true;
 }
@@ -1604,7 +1605,10 @@ static void i40e_reuse_rx_page(struct i40e_ring *rx_ring,
 	rx_ring->next_to_alloc = (nta < rx_ring->count) ? nta : 0;
 
 	/* transfer page from old buffer to new buffer */
-	*new_buff = *old_buff;
+	new_buff->dma		= old_buff->dma;
+	new_buff->page		= old_buff->page;
+	new_buff->page_offset	= old_buff->page_offset;
+	new_buff->pagecnt_bias	= old_buff->pagecnt_bias;
 }
 
 /**
@@ -1656,14 +1660,15 @@ static bool i40e_can_reuse_rx_page(struct i40e_rx_buffer *rx_buffer,
 #if (PAGE_SIZE >= 8192)
 	unsigned int last_offset = PAGE_SIZE - I40E_RXBUFFER_2048;
 #endif
+	unsigned int pagecnt_bias = rx_buffer->pagecnt_bias--;
 
 	/* Is any reuse possible? */
 	if (unlikely(!i40e_page_is_reusable(page)))
 		return false;
 
 #if (PAGE_SIZE < 8192)
 	/* if we are only owner of page we can reuse it */
-	if (unlikely(page_count(page) != 1))
+	if (unlikely(page_count(page) != pagecnt_bias))
 		return false;
 
 	/* flip page offset to other buffer */
@@ -1676,9 +1681,14 @@ static bool i40e_can_reuse_rx_page(struct i40e_rx_buffer *rx_buffer,
 		return false;
 #endif
 
-	/* Inc ref count on page before passing it up to the stack */
-	get_page(page);
-
+	/* If we have drained the page fragment pool we need to update
+	 * the pagecnt_bias and page count so that we fully restock the
+	 * number of references the driver holds.
+	 */
+	if (unlikely(pagecnt_bias == 1)) {
+		page_ref_add(page, USHRT_MAX);
+		rx_buffer->pagecnt_bias = USHRT_MAX;
+	}
 	return true;
 }
 
@@ -1725,7 +1735,6 @@ static bool i40e_add_rx_frag(struct i40e_ring *rx_ring,
 			return true;
 
 		/* this page cannot be reused so discard it */
-		__free_pages(page, 0);
 		return false;
 	}
 
@@ -1819,6 +1828,8 @@ struct sk_buff *i40e_fetch_rx_buffer(struct i40e_ring *rx_ring,
 		/* we are not reusing the buffer so unmap it */
 		dma_unmap_page_attrs(rx_ring->dev, rx_buffer->dma, PAGE_SIZE,
 				     DMA_FROM_DEVICE, I40E_RX_DMA_ATTR);
+		__page_frag_cache_drain(rx_buffer->page,
+					rx_buffer->pagecnt_bias);
 	}
 
 	/* clear contents of buffer_info */

drivers/net/ethernet/intel/i40e/i40e_txrx.h

@@ -258,7 +258,12 @@ struct i40e_tx_buffer {
 struct i40e_rx_buffer {
 	dma_addr_t dma;
 	struct page *page;
-	unsigned int page_offset;
+#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
+	__u32 page_offset;
+#else
+	__u16 page_offset;
+#endif
+	__u16 pagecnt_bias;
 };
 
 struct i40e_queue_stats {

drivers/net/ethernet/intel/i40evf/i40e_txrx.c

@@ -526,7 +526,7 @@ void i40evf_clean_rx_ring(struct i40e_ring *rx_ring)
 				     PAGE_SIZE,
 				     DMA_FROM_DEVICE,
 				     I40E_RX_DMA_ATTR);
-		__free_pages(rx_bi->page, 0);
+		__page_frag_cache_drain(rx_bi->page, rx_bi->pagecnt_bias);
 
 		rx_bi->page = NULL;
 		rx_bi->page_offset = 0;
@@ -671,6 +671,7 @@ static bool i40e_alloc_mapped_page(struct i40e_ring *rx_ring,
 	bi->dma = dma;
 	bi->page = page;
 	bi->page_offset = 0;
+	bi->pagecnt_bias = 1;
 
 	return true;
 }
@@ -966,7 +967,10 @@ static void i40e_reuse_rx_page(struct i40e_ring *rx_ring,
 	rx_ring->next_to_alloc = (nta < rx_ring->count) ? nta : 0;
 
 	/* transfer page from old buffer to new buffer */
-	*new_buff = *old_buff;
+	new_buff->dma		= old_buff->dma;
+	new_buff->page		= old_buff->page;
+	new_buff->page_offset	= old_buff->page_offset;
+	new_buff->pagecnt_bias	= old_buff->pagecnt_bias;
 }
 
 /**
@@ -1018,14 +1022,15 @@ static bool i40e_can_reuse_rx_page(struct i40e_rx_buffer *rx_buffer,
 #if (PAGE_SIZE >= 8192)
 	unsigned int last_offset = PAGE_SIZE - I40E_RXBUFFER_2048;
 #endif
+	unsigned int pagecnt_bias = rx_buffer->pagecnt_bias--;
 
 	/* Is any reuse possible? */
 	if (unlikely(!i40e_page_is_reusable(page)))
 		return false;
 
 #if (PAGE_SIZE < 8192)
 	/* if we are only owner of page we can reuse it */
-	if (unlikely(page_count(page) != 1))
+	if (unlikely(page_count(page) != pagecnt_bias))
 		return false;
 
 	/* flip page offset to other buffer */
@@ -1038,8 +1043,14 @@ static bool i40e_can_reuse_rx_page(struct i40e_rx_buffer *rx_buffer,
 		return false;
 #endif
 
-	/* Inc ref count on page before passing it up to the stack */
-	get_page(page);
+	/* If we have drained the page fragment pool we need to update
+	 * the pagecnt_bias and page count so that we fully restock the
+	 * number of references the driver holds.
+	 */
+	if (unlikely(pagecnt_bias == 1)) {
+		page_ref_add(page, USHRT_MAX);
+		rx_buffer->pagecnt_bias = USHRT_MAX;
+	}
 
 	return true;
 }
@@ -1087,7 +1098,6 @@ static bool i40e_add_rx_frag(struct i40e_ring *rx_ring,
 			return true;
 
 		/* this page cannot be reused so discard it */
-		__free_pages(page, 0);
 		return false;
 	}
 
@@ -1181,6 +1191,8 @@ struct sk_buff *i40evf_fetch_rx_buffer(struct i40e_ring *rx_ring,
 		/* we are not reusing the buffer so unmap it */
 		dma_unmap_page_attrs(rx_ring->dev, rx_buffer->dma, PAGE_SIZE,
 				     DMA_FROM_DEVICE, I40E_RX_DMA_ATTR);
+		__page_frag_cache_drain(rx_buffer->page,
+					rx_buffer->pagecnt_bias);
 	}
 
 	/* clear contents of buffer_info */

drivers/net/ethernet/intel/i40evf/i40e_txrx.h

@@ -244,7 +244,12 @@ struct i40e_tx_buffer {
 struct i40e_rx_buffer {
 	dma_addr_t dma;
 	struct page *page;
-	unsigned int page_offset;
+#if (BITS_PER_LONG > 32) || (PAGE_SIZE >= 65536)
+	__u32 page_offset;
+#else
+	__u16 page_offset;
+#endif
+	__u16 pagecnt_bias;
 };
 
 struct i40e_queue_stats {